Evolution And Controlling Factors Of Sedimentary Sequence Of Zhujiang Formation Along The Shelf Slope-break Zone On The Northwest Of Baiyun Depression

Baiyun depression is an important oil and gas-bearing district of the Pearl River Mouth Basin.With the guidance of the theory of Sequence Stratigraphy,Sedimentology,Geology and Seismic Sedimentology,Structural and Seismic Geomorphology,and based on the research of single well and multi-well core analysis,well-seismic cutting,2D and 3D seismic reflection data,nannofossil and foraminifer,third-order sequences of Zhujiang.Zhujiang Formation in the research area is divided into four third-order sequences(SQzj1?SQzj2?SQzj3?SQzj4),every third-order sequence was divided in to 3-4 systems tracts.In SQzj2 low order systems tract,early and late periods of low order systems tract were recognized based on seismic reflection characteristic,log presentation and seismic attributions.In the chronostratigraphic framework,primary depositional systems were described which includes braided river depositional system,delta depositional system,offshore and shallow sea depositional system,continental shelf depositional system and abyssal fan depositional system,etc.Research shows that there are two set of delta deposit and two times of downcutting channels in the third-order sequence SQzj2.Based on the clarification of characteristic sequence structure and depositional system,the dominances of the palaeogeomorphology of the basin,the changes of the sea level,the direction of the provenance and the sectonic process to the abundance of depositional sequence were developed,which indicates that it is the back and forth of the sea water in the shelf that controls the basic characteristic of sequence structures.It was concluded that Zhujiang formation has two different provenances based on the research of zircon dating.The favorable sand bodies are predicted in the key sequence systems.